Fine carbon fibers such as the carbon nano structures, typically, for example, carbon nanotubes (Hereafter, it is referred to as “CNT”) has been developed, and the attempts to try to improve physical properties of various matrices by adding the fine carbon fibers into various matrices so as to form composite materials has been performed widely in recent years.
The graphite layers that make up the carbon nano structures are materials normally comprised of regular arrays of six-membered rings whose structures can bring about specific electrical properties, as well as chemically, mechanically, and thermally stable properties. As long as such fine carbon fibers can retain such properties upon combining and dispersing into a matrix, their usefulness as an electroconductive or antistatic material can be expected.
However, cohesion by the van der Waals force between adjacent CNTs is caused easily in such CNTs, and in particular, single wall carbon nanotubes (Hereafter, the single wall carbon nanotube is also referred to as “SWCNT”) because the all of the constituent atoms thereof are surface atoms. Thus, it has been known that strong cohesion (bundle) structure consisting of plural CNTs has been already formed at the time of synthesis of CNTs. Therefore, when the CNTs are used as they are, dispersion of CNTs in a film formable composition would hardly progress, and which would be followed by inferior properties of the film formed thereby.
In addition, the fine carbon fibers show very bad handling property because the fine carbon fibers are supplied as an aggregate of fluffy or powdery form having a very low bulk density, and have a problem that the fine fibers are easily airborne around the working environment atmosphere when using them.
In order to solve such a handling problem, some attempts have been made to add the fine carbon fibers into various resins so as to pelletize or to make them up into a masterbatch before using them. The handling property has been improved certainly by the pelletization or masterbatching. When the pellet or masterbatch is further added and diluted into a resin matrix or the like, however, the dispersion of fine carbon fibers have not progressed well, with the result that the fine carbon fibers have existed as their aggregated state of some degree in the matrix.
On the other hand, various researches has been advanced as a technology to improve the dispersion property of the fine carbon fibers. For instance, various methods, such as (1) methods for dispersing fine carbon fibers to a dispersion medium by a physical treatment such as supersonic wave, various stirring devices or the like (for instance, Patent Literature 1, etc.); (2) methods for dispersing fine carbon fibers to a dispersion medium by modifying chemically the fine carbon fibers (for instance, Patent Literature 2, etc.); and (3) methods for dispersing carbon nano tubes to a dispersion medium by using a dispersing agent such as surfactant or the like (for instance, see Patent Literature 3) have been reported.
Since many of the above mentioned technologies to improve the dispersion property of the fine carbon fibers provide the fine carbon fibers as a dispersion form of them in a liquid dispersion medium, the handling property of the fine carbon fibers can be improved up to a certain extent as compared with the case of the fluffy or powdery form.
Even though the liquid dispersion is formed, however, the handling property of the fine carbon fibers does not still attain to a sufficient level. Further, depending on the kind of the matrix to be complexed with the fine carbon fibers, the liquid dispersion medium would become an obstacle, and a phase of requiring removal of the dispersion medium would arise.
On the other hand, in the case of manufacturing solid products, such as electron emitter, by using such fine carbon fibers, it has been widely proposed that the fine carbon fibers are made into a paste form by adding and dispersing them to resinous component, surfactant, thickener, etc. (for instance, see Patent Literatures 4 and 5, etc.)
Such a resinous paste including fine carbon resin content paste shows a good handling property and the dispersibility of the fine carbon fibers in the paste attains an ample level. As for the paste, however, it is out of consideration that the paste is further added to a dispersion medium or the like so as to redisperse the fine carbon fibers into the dispersion medium. Because, the paste is prepared, with the aim of solidifying it as is, after molding into a prescribed shape for a product intended. In addition, as a matter of fact, the dispersibility of the fine carbon fibers in the paste system is maintained to a certain extent with the consistency of the paste. Thus, even if the paste is added into an appropriate dispersion medium, a result that the cohesiveness of the fine carbon fibers becomes strengthened would be liable to occur, instead of obtaining a dispersed state of individually isolated fine carbon fibers.    [Patent Literature 1] JP 2004-256964, A    [Patent Literature 2] JP 2006-265151, A    [Patent Literature 3] JP 2005-263608, A    [Patent Literature 4] JP 2005-122930, A    [Patent Literature 5] JP 2006-182601, A[Disclosure of the Invention][Problems to be Solved by the Invention]
Therefore, the present invention aims to provide a redispersible agglomerate of fine carbon fibers which has a good handling property, and which can easily form the dispersed state of individually isolated fine carbon fibers when it is added to any of various dispersion media; and a method for manufacturing thereof.
[Means for Solving the Problem]
The present invention that solves the above-mentioned problem is a redispersible agglomerate of fine carbon fibers, which is characterized in that it is obtained by adding the fine carbon fibers and a dispersing agent which shows solid state at least at ordinary temperature (20±10° C). into an aqueous dispersion medium, and then removing the dispersion medium from a dispersion system where the carbon fibers are isolated individually and dispersed in the dispersion medium; and that the carbon fibers are got together and solidified in the agglomerate while each carbon fiber maintains its isolated dispersibility;
wherein the carbon content is in the range of 0.01-99.5% by weight, the dispersing agent content is in the range of 0.1-99.5% by weight, and the moisture content is in the range of less than 10% by weight, based on the total weight of the agglomerate; and
wherein the dispersing agent is one member selected from the group consisting of (1) surfactants capable of forming spheroidal, cylindrical, or tabular micelles of 5-2000 nm in diameter in an aqueous solution; (2) water-soluble high polymers having a weight average molecular weight in the range of 10,000-50,000,000; and (3) a combination of cyclodextrin and fullerene.
The present invention also provides the redispersible agglomerate of fine carbon fibers, wherein the redispersible agglomerate of fine carbon fibers is formed into a block or granules.
Further, the present invention provides the redispersible agglomerate of fine carbon fibers, wherein each fine carbon fiber comprises tubular graphene sheets layered in a direction orthogonal to the axis of the fine carbon fiber,
wherein the tubular graphene sheets include polygonal cross sections in a direction orthogonal to the axis of the fine carbon fiber, wherein a maximum diameter of the cross sections is in the range of 15 to 100 nm, an aspect ratio of the fine carbon fiber is not more than 105, and ID/IG of the fine carbon fiber as determined by Raman spectroscopy at 514 nm is not more than 0.1.
Further, the present invention provides the redispersible agglomerate of fine carbon fibers, wherein carbon fibrous structures are used as the fine carbon fibers,
each carbon fibrous structure comprising a three dimensional network of carbon fibers, said carbon fibers each having an outside diameter of 1-100 nm, said carbon fibrous structure further comprising a granular part with which said carbon fibers are bound in a state that said carbon fibers extend outwardly from the granular part, and the granular part being produced in a growth process of the carbon fibers; and,
wherein the dispersion system where the carbon fibers are isolated individually and dispersed in the dispersion medium is formed by a dispersion treatment of using a media mill.
The present invention that solves the above-mentioned problem is also a method for manufacturing redispersible agglomerate of fine carbon fibers, wherein the carbon fibers are got together and solidified while each carbon fiber maintains its isolated dispersibility,
which method comprises adding (A) the fine carbon fibers and (B) a dispersing agent into an aqueous dispersion medium, wherein the dispersing agent is one member selected from the group consisting of (1) surfactants capable of forming spheroidal, cylindrical, or tabular micelles of 5-2000 nm in diameter in an aqueous solution, (2) water-soluble high polymers having a weight average molecular weight in the range of 10,000-50,000,000, and (3) a combination of cyclodextrin and fullerene;
isolating the carbon fibers individually and dispersing them in the dispersion medium to form a dispersion system; and then
removing the dispersion medium from the dispersion system.
The present invention also provides method for manufacturing redispersible agglomerate of fine carbon fibers, wherein the dispersion medium removes from a dispersion system at a temperature in the range of −197° C. to 450° C.
The present invention also provides method for manufacturing redispersible agglomerate of fine carbon fibers, wherein carbon fibrous structures are used as the fine carbon fibers,
each carbon fibrous structure comprising a three dimensional network of carbon fibers, said carbon fibers each having an outside diameter of 1-100 nm, said carbon fibrous structure further comprising a granular part with which said carbon fibers are bound in a state that said carbon fibers extend outwardly from the granular part, and the granular part being produced in a growth process of the carbon fibers; and,
wherein the dispersion system where the carbon fibers are isolated individually and dispersed in the dispersion medium is formed by a dispersion treatment of using a media mill.
[Effect of the Invention]
With respect to the redispersible agglomerate of fine carbon fibers according to the present invention, since the fine carbon fibers are got together and solidified in the agglomerate while each carbon fiber maintains its isolated dispersibility, it can show an excellent handling property, the isolated dispersibility can be maintained stably for a long time, and the problem that the fine fibers are airborne around the working environment atmosphere when using or transporting the fine carbon fibers is not caused. In addition, when the agglomerate of fine carbon fibers is added to any of various media, the agglomerate can separate easily and promptly into mutually independent carbon fibers in the medium and disperse the carbon fibers uniformly in the medium. Therefore, the agglomerate of fine carbon fibers can be suitably used for various usages in which the fine carbon fibers are complexed into various materials to obtain desired products.